From Longman Dictionary of Contemporary Englishjump the gunjump the gunEARLYto start doing something too soon, especially without thinking about it carefully → jump
Examples from the Corpus
jump the gun• Miller is young, and comparing him to the great quarterbacks is jumping the gun.• But I have jumped the gun.• Suppose some broker was able to anticipate the radio sign from Chicago, then he could jump the gun.• Aren't we jumping the gun a bit?• The owners are constantly carping about runaway salaries, then fall over themselves to jump the gun and up the ante.• It is unlikely that Boris Yeltsin would be implementing those reforms if we had jumped the gun, as the Opposition wanted.• The new squad will officially be in existence on Monday anyway, so we're only jumping the gun by six days.• But we are jumping the gun here.• Surely it's jumping the gun to buy the ring before you've even asked her to marry you?• I think it would be jumping the gun to sign the agreement at this stage. 